1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus and more particularly to a magnetic recording and reproducing apparatus improved such that no disturbance appears in a jointing portion of a picture corresponding to a jointing portion of a picture recording on a magnetic tape at the time of reproduction.
2. Description of the Prior Art
In a conventional home magnetic video reproducing apparatus and a magnetic video recording and reproducing apparatus having a picture recording function, there are generally employed a rotating head system, a helical scanning system and an azimuth system. In the rotating head system, e.g., two video heads are mounted on the circumference of a rotating drum to be separated from each other at an angle of 180.degree.. In the helical scanning system, a magnetic tape is made to travel aslant with respect to the video heads. In the azimuth system, gaps of the two video heads are provided at angles different from each other, so that angles of video signals recorded in the magnetic tape vary with the video heads. These three systems are disclosed in detail in, e.g., U.S. Pat. No. 4,463,390 issued on July 31, 1984 to Yoshio Koga et al. The referenced U.S. patent is incorporated herein by reference thereto.
As a magnetic tape travelling control system in a conventional magnetic recording and reproducing apparatus, a system using a control signal, a system using a pilot signal and the like have been proposed.
First, a control system using a control signal will be described.
FIG. 1 is a diagram showing a state of a magnetic tape recorded by a magnetic recording and reproducing apparatus of a helical scanning system where control tracks other than video signal tracks are provided. In FIG. 1, a video signal track 2 is obliquely recorded on a magnetic tape 1 for one field usually regarded as a unit and a control signal 3 is recorded at fixed intervals in a tape travelling direction. The control signal 3 serves to control the travel of the tape so that a video signal magnetic head 5 can precisely scan the video signal track 2 at the time of reproduction. In the following description, a signal before it is recorded on the magnetic tape 1 is referred to as a to-be-recorded control signal, a signal recorded on the magnetic tape 1 is referred to as a recorded control signal 3 and a signal reproduced from the magnetic tape 1 is referred to as a reproduced control signal J. All these control signals are generally and simply referred to as a control signal.
Generally, the control signal 3 is obtained by 1/2 frequency division of a vertical synchronizing signal of a video signal to be recorded. In consequence, the travelling state of the magnetic tape 1 is controlled so that in the reproducing operation the time when a control head 6 detects the control signal 3 coincides with the time when the video signal magnetic head 5 comes in the vicinity of a leading edge of the video signal track 2 (namely, in a portion where the vertical synchronizing signal is recorded).
If the magnetic tape 1 is temporarily stopped at an arbitrary time during a recording operation and then operated again at an arbitrary timing to immediately restart the recording operation, a disturbance would appear in a reproduced picture at the recorded jointing portion, since the recording phase of the video signal track 2 becomes different or the angle of inclination of the video signal track 2 is changed at such jointing portion. For example, when the magnetic tape 1 is temporarily stopped, the travelling locus of the video signal magnetic head 5 becomes as shown by the dotted lines 4 in FIG. 1. In order to prevent such disturbance of a picture in the jointing portion, an operation as described below is performed in a servo control system.
When a temporary stop instruction is provided during the recording operation, the recording operation is immediately stopped and the magnetic tape 1 is moved by a certain amount in the backward direction. Then, movement of the magnetic tape 1 is stopped and the magnetic tape 1 is in a waiting state for recording.
After that, when the temporary stop instruction is cancelled, the magnetic tape 1 starts to move in the forward direction. At this time, control is made such that until before the recording operation is started a reproduced control signal J from a control track of the magnetic tape 1 is synchronized with a vertical synchronizing signal to be used as a reference for a video signal which is to be newly recorded. More specifically, after the phase of the previously recorded video signal track is made to coincide with the phase of a video signal track to be newly recorded, the record mode is selected to restart the recording operation. Thus, continuous recording is performed so that a disturbance may not appear at the time of reproduction in a jointing portion between a previously recorded picture and a newly recorded picture.
Next, as an example of the system using a pilot signal, a 4f pilot signal control system will be described.
FIG. 2 is a diagram showing a relation between the video signal tracks formed obliquely in a longitudinal direction of a magnetic tape 7 and the pilot signals recorded in a manner overlapping with a video signal in the respective video signal tracks. Referring to FIG. 2, in the video signal tracks F.sub.1, F.sub.2, F.sub.3 and F.sub.4, the pilot signals having frequencies f.sub.1, f.sub.2, f.sub.3 and f.sub.4, respectively, are recorded in an overlapping manner. These frequencies satisfy the conditions of EQU .vertline.f.sub.2 -f.sub.1 .vertline..perspectiveto..vertline.f.sub.3 -f.sub.4 .vertline.=f.sub.a, EQU .vertline.f.sub.1 -f.sub.4 .vertline..perspectiveto..vertline.f.sub.2 -f.sub.3 .vertline.=f.sub.b, f.sub.a .noteq.f.sub.b.
Now let us assume a case in which the magnetic head 8 tracks the video signal track F.sub.1 on the magnetic tape 7 as shown in FIG. 2, for example. A pilot signal component detected by the magnetic head 8 includes not only a pilot signal of the frequency f.sub.1 superimposed on the video signal track F.sub.1 but also pilot signals superimposed on the two adjacent tracks (F.sub.2 and F.sub.4 in the example of FIG. 2) by a side read effect, cross-talk or the like. The magnitude of the pilot signals detected from these adjacent tracks becomes large according to the increase of deviation from the center of the video signal track tracked by the magnetic head 8. As a result, the magnitude of .vertline.f.sub.2 -f.sub.1 .vertline. and that of .vertline.f.sub.4 -f.sub.1 .vertline. are voltage converted and, based on the obtained values, a direction of deviation from the center of the video signal track is detected, so that an amount of deviation from the center of the video signal track is detected according to a difference component. The error component thus detected is fed back to the servo control system, whereby the travel of the magnetic tape is controlled.
However, as in the case of a control system using a control signal, a magnetic recording and reproducing apparatus using such a pilot signal control system involves a disadvantage that it does not have a continuous recording function without causing disturbance at the time of reproduction in a jointing portion between a previously recorded picture and a newly recorded picture.